Methods to supply power to a load using magnetic coupling mutually between coils by electromagnetic induction include, for example, non-contact power supply. Its principle is to form a so-called transformer by coupling a plurality of coils magnetically through a space, and to exchange power using electromagnetic induction between the coils.
For example, a primary side coil corresponding to the power supply source is arranged in a rail shape as a power supply line, and a secondary side coil and a power receiving circuit area integrated to constitute a mobile body, and also, the primary side coil and the secondary side coil are made to face each other. Accordingly, non-contact power supply may be conducted to the mobile object moving along the power supply line.
Here, FIG. 28 illustrates a non-contact power supply device described in Japanese Laid-open Patent Publication No. 2002-354711. In FIG. 28, to the both ends of a high frequency power source 100, a primary side power supply line 110 as a coil is connected. To the primary side power supply line 110, a power receiving coil 120 is coupled magnetically, and the primary side power supply line 110 and the power receiving coil 120 form a sort of transformer.
The both ends of the power receiving coil 120 are connected to a pair of AC (alternating-current) terminals of a full-wave rectifier circuit 10 through a resonance capacitor Cr. The power receiving coil 120 and the resonance capacitor Cr constitute a serial resonance circuit.
The full-wave rectifier circuit 10 is configured by bridge-connecting diodes Du, Dv, Dx, Dy.
To a pair of DC (direct-current) terminals of the full-wave rectifier circuit 10, a constant voltage control circuit 20 is connected which performs control so as to make the DC output voltage of the full-wave rectifier circuit 10 become equal to the reference voltage value. The constant voltage control circuit 20 is, for example, configured of a step-up chopper circuit which is formed, for example, of a reactor L1, a diode D1, a smoothing capacitor C0 and a semiconductor switch SW1, and to the both ends of the smoothing capacitor C0, a load R is connected.
In FIG. 28 a control device for switching the semiconductor switch SW1 is omitted.
In the conventional art of FIG. 28, the high frequency power source 100 flows a high frequency current into the primary side power supply line 110, the high frequency power supplied through the power receiving coil 120 is input into the full-wave rectifier circuit 10 and converted into DC power.
Generally, with this type of non-contact power supply device, due to a cause such as the change of the gap length between the primary side power supply line 110 and the power receiving coil 120 and the positional displacement of them, the voltage induced in the power receiving coil 120 changes, and accordingly, the DC output voltage of the full-wave rectifier circuit 10 fluctuates. In addition, the characteristics of the load R are also a cause of the fluctuation of the DC output power of the full-wave rectifier circuit 10.
For this reason, in the conventional art of FIG. 28, the DC output voltage of the full-wave rectifier circuit 10 is controlled to a constant value by the constant voltage control circuit 20.
In the non-contact power supply device, as the frequency of the current supplied through the coil becomes higher, the excitation inductance necessary for power transmission may be smaller, and the coil and the core placed in its periphery may be made smaller. However, in a power converter which configures the high frequency power source device or the power receiving circuit, as the frequency of the current flowing in the circuit becomes higher, the switching loss of the semiconductor switch increases and the power supply efficiency decreases. For this reason, the frequency of the power fed in a non-contact power is generally set to several [kHz] to several tens of [kHz].
The non-contact power supply device illustrated in FIG. 28, especially, the power receiving circuit in the subsequent stage of the resonance capacitor Cr has the following problems.
(1) Since the power receiving circuit is configured by the full-wave rectifier circuit 10 and the constant voltage control circuit 20, the entire circuit becomes large, causing an expansion of the installation space and an increase in the cost.
(2) In addition to the diodes Du, Dv, Dx, Dy of the full-wave rectifier circuit 10, losses occur in the reactor L1, the semiconductor switch SW1, the diode D1 of the constant voltage control circuit 20, and these losses is a factor for a decrease in the power supply efficiency.
As a conventional art to solve the problems described above, a non-contact power supply device and its control method described in Japanese Laid-open Patent Publication No. 2012-125138 have already been proposed by the inventors.
FIG. 29 illustrates a non-contact power supply device described in Japanese Laid-open Patent Publication No. 2012-125138.
In FIG. 29, 310 is a power receiving circuit. The power receiving circuit 310 includes semiconductor switches Qu, Qx, Qv, Qy, diodes Du, Dx, Dv, Dy, capacitors Cx, Cy, and the smoothing capacitor C0. The semiconductor switches Qu, Qx, Qv, Qy are bridge-connected. The diodes Du, Dx, Dv, Dy are respectively connected in an inverse-parallel manner to the respective switches Qu, Qx, Qv, Qy. The capacitors Cx, Cy are respectively connected in parallel to the switches Qx, Qy of the lower arm. The smoothing capacitor C0 is connected between DC terminals of a bridge circuit (full bridge inverter) configured by these elements. Between the AC terminals of the bridge circuit, a series circuit of a resonance capacitor Cr and a power receiving coil 120 is connected, and to the both ends of the smoothing capacitor C0, a load R is connected.
A control device 200 generates a driving signal for switching the semiconductor switches Qu, Qx, Qv, Qy. The control device 200 generates the driving signal based on a current i of the power receiving coil 120 detected by a current detection unit CT and a voltage between DC terminals (DC output voltage) Vo of the power receiving circuit 310.
In this non-contact power supply device, by controlling the semiconductor switches Qu, Qx, Qv, Qy the voltage v between AC terminals of the bridge circuit is controlled to a positive-negative voltage whose peak value is the voltage Vo between DC terminals. The supply power from the primary side power supply line 110 to the power receiving circuit 310 is the product of the current i of the power receiving coil 120 and the voltage v between AC terminals. By the control of the phase of the driving signal of the semiconductor switches Qu, Qx, Qv, Qy based on the voltage Vo between DC terminals performed by the control device 200, the constant control of the supply power, that is, the voltage Vo between DC terminals is enabled.
In addition, by configuring the power receiving circuit 310 by the bridge circuit configured by the switches Qu, Qx, Qv, Qy and the diodes Du, Dx, Dv, Dy, an operation to maintain the power constant even in a case in which the load R is a regenerative load is enabled.
According to this non-contact power supply device, without using constant voltage control circuit as in the conventional art of FIG. 28, the voltage Vo between DC terminals may be controlled to be constant by the phase control of the driving signal of the semiconductor switches Qu, Qx, Qv, Qy. In addition, the power receiving circuit 310 may be configured by the bridge circuit and the smoothing capacitor C0 only. Accordingly, the circuit configuration may be made simpler and smaller, and its cost may be reduced, and also, the loss may be reduced by reducing the number of component parts, to enable a high-efficiency, stable non-contact power supply. In addition, by the charging and discharging action of the capacitors Cx, Cy, the so-called soft switching is performed, making it possible to reduce the switching loss to further increase the efficiency.
However, in the conventional art described in Japanese Laid-open Patent Publication No. 2012-125138, the current i of the power receiving coil 120 becomes a leading phase to the fundamental wave component of the voltage v between AC terminals. For this reason, there is a problem that the input power factor of the power receiving circuit 310 decreases, which causes an increase in the loss of the entire device, being a factor that hinders further downsizing.
Then, the applicant has already proposed, as Japanese Patent Application No. 2013-071432 (hereinafter, referred to as the earlier application), a non-contact power supply device with an improvement in the input power factor of the power receiving circuit (hereinafter, referred to as the earlier application invention).
FIG. 30 is a circuit diagram of the earlier application invention.
In FIG. 30, a power receiving circuit 320 includes switches Qu, Qx, Qv, Qy, diodes Du, Dx, Dv, Dy and a smoothing capacitor C0. The switches Qu, Qx, Qv, Qy, are bridge-connected. The diodes Du, Dx, Dv, Dy are respectively connected to the respective switches Qu, Qx, Qv, Qy, in an inverse-parallel manner. The smoothing capacitor C0 is connected between a pair of DC terminals of a bridge circuit configured by these elements. Between a pair of AC terminals of the bridge circuit, a series circuit of a resonance capacitor Cr and a power receiving coil 120 is connected, and to the both ends of the smoothing capacitor C0, a load R is connected. 100 is a high frequency power source, and 110 is a primary side power supply line.
Meanwhile, the control device 200 generates and output a driving signal of the switches Qu, Qx, Qv, Qy, based on the voltage Vo between DC terminals and the current i of the power receiving coil 120 detected by a current detecting unit CT. While it is not illustrated in the drawing, the voltage Vo between DC terminals is detected by a known voltage detecting unit such as a DC voltage detector.
Next, in FIG. 30, operations in a case of supplying power from the power receiving coil 120 to the load R are explained.
FIG. 31 illustrates the current i of the power receiving coil 120, the voltage v between AC terminals of the bridge circuit, its fundamental wave component v′, and the driving signals of the switches Qu, Qx, Qv, Qy. The switches Qu, Qx, Qv, Qy performs a switching operation at a constant frequency synchronized with the current i. In FIG. 31, ZCP′ indicates the zero crossing point of the current i.
The operations in the respective time periods (1) through (4) in FIG. 31 are explained below.
(1) Time period (1) (switches Qu, Qy are turned on): The current i flows in the route of the resonance capacitor Cr→the diode Du→the smoothing capacitor C0→the diode Dy→the power receiving coil 120, and the voltage v becomes, as illustrated in the drawing, the positive voltage level corresponding to the voltage Vo between DC terminals. In this period, the smoothing capacitor C0 is charged by the current i.(2) Time period (2) (switches Qx, Qy are turned on): The current i flows in the route of the resonance capacitor Cr→switches Qx→the diode Dy→the power receiving coil 120, and the voltage v becomes, as illustrated in the drawing, the zero voltage level.(3) Time period (3) (switches Qu, Qv are turned on): The current i flows in the route of the resonance capacitor Cr→the power receiving coil 120→the diode Dv→switches Qu, and the voltage v becomes, as illustrated in the drawing, the zero voltage level.(4) Time period (4) (switches Qx, Qv are turned on): The current i flows in the route of the resonance capacitor Cr→the power receiving coil 120→the diode Dv→the smoothing capacitor C0→the diode Dx, and the voltage v becomes, as illustrated in the drawing, the negative voltage level corresponding to the voltage Vo between DC terminals. In this period, the smoothing capacitor C0 is charged by the current i.
After this, changing to the switching mode in the period (1), similar operations are repeated.
As is apparent from FIG. 31, according to the earlier application invention, the control device 200 performs the switching control of the semiconductor switches Qu, Qx, Qv, Qy. Accordingly, the voltage v between AC terminals of the bridge circuit is controlled to be zero voltage only in a time period α before and after one of the zero crossing points ZCP′ of the current i flowing in the power receiving coil 120, and to be a positive-negative voltage whose peak value is the voltage Vo between DC terminals in the other time periods. The supply power from the primary side power supply line 110 to the power receiving circuit 320 is the product of the current i and the voltage v. Then, by the adjustment of the driving signals of the switches Qu, Qx, Qv, Qy based on the detected value of the voltage Vo between DC terminals by the control device 200, the control of the supply power, that is, the constant control of the voltage Vo between DC terminals becomes possible.
At this time, as illustrated in FIG. 31, the phase difference between the current i flowing in the power receiving coil 120 and the fundamental wave component v′ of the voltage v between AC terminals of the bridge circuit is 0°, the input power factor of the power receiving circuit 320 may be set as 1.
In the earlier application invention, when the resonance frequency by the power receiving coil 120 and the resonance capacitor Cr completely matches the power source frequency, the input power factor of the power receiving circuit 320 becomes 1, but when the resonance frequency deviates from the power supply frequency, the input power factor of the power receiving circuit 320 decreases. The reason for it is explained below.
FIG. 32 illustrates an input side equivalent circuit of the power receiving circuit 320 in a case in which the resonance frequency by the power receiving coil 120 and the resonance capacitor Cr deviates from the power source frequency. In FIG. 32, a voltage vin induced in the power receiving coil 120 is expressed as an AC power source, and a numeral 400 represents the impedance corresponding to the power receiving circuit 320 and the load R. However, generally, with respect to the load R, other impedances may be ignored, and therefore, the numeral 400 may be regarded as a pure resistance corresponding to the load R.
In addition, FIG. 33 illustrates the operating waveform of the current i flowing in the power receiving coil 120, the induced voltage vin of the power receiving coil 120, the voltage v between AC terminals of the bridge circuit and the fundamental wave component v′ of the voltage v between AC terminals.
As illustrated in FIG. 32, the inductance of the power receiving coil 120 is assumed to be L[H], and the capacitance of the resonance capacitor Cr is assumed to be Cr[F] in the same manner as the numeral of the component. When the power source frequency is further assumed as fs[Hz], a combined inductance Ls[H] of the inductance L and the resonance capacitor Cr is defined by the expression (1).
                              2          ⁢          π          ⁢                                          ⁢                      f            s                    ⁢                      L            s                          =                              2            ⁢            π            ⁢                                                  ⁢                          f              s                        ⁢            L                    -                      1                          2              ⁢              π              ⁢                                                          ⁢                              f                s                            ⁢                              C                r                                                                        (        1        )            
Meanwhile, the resonance frequency of a resonance circuit configured by the power receiving coil 120 and the resonance capacitor Cr is expressed by the expression (2).
                              f          c                =                  1                      2            ⁢            π            ⁢                                          LC                r                                                                        (        2        )            
Therefore, when fc=fs, Ls=0 is established, and when fc≠fs, Ls≠0 is established.
In addition, according to the control method presented in FIG. 31, the phase of v′ matches the phase of i. For this reason, when the current i of the power receiving coil 120 is expressed as I sin ωt, v′ may be expressed as V′ sin ωt.
In this regard, vin is expressed by the sum of the fundamental wave component v′ of v and vL from FIG. 32, as in the expression (3).
                                                                                                              v                    in                                    ⁡                                      (                                          ω                      ⁢                                                                                          ⁢                      t                                        )                                                  =                                ⁢                                                                            v                      ′                                        ⁡                                          (                                              ω                        ⁢                                                                                                  ⁢                        t                                            )                                                        +                                                            v                      L                                        ⁡                                          (                                              ω                        ⁢                                                                                                  ⁢                        t                                            )                                                                                                                                              =                                ⁢                                                                            V                      ′                                        ⁢                                          sin                      ⁡                                              (                                                  ω                          ⁢                                                                                                          ⁢                          t                                                )                                                                              +                                                            j                      ⁡                                              (                                                  2                          ⁢                          π                          ⁢                                                                                                          ⁢                                                      f                            s                                                                          )                                                              ⁢                                          L                      s                                        ⁢                    I                    ⁢                                                                                  ⁢                                          sin                      ⁡                                              (                                                  ω                          ⁢                                                                                                          ⁢                          t                                                )                                                                                                                                                                    =                                ⁢                                                                            V                      ′                                        ⁢                                          sin                      ⁡                                              (                                                  ω                          ⁢                                                                                                          ⁢                          t                                                )                                                                              +                                      2                    ⁢                    π                    ⁢                                                                                  ⁢                                          f                      s                                        ⁢                                          L                      s                                        ⁢                    I                    ⁢                                                                                  ⁢                                          cos                      ⁡                                              (                                                  ω                          ⁢                                                                                                          ⁢                          t                                                )                                                                                                                                                                    =                                ⁢                                                      V                    a                                    ⁢                                      sin                    ⁡                                          (                                                                        ω                          ⁢                                                                                                          ⁢                          t                                                +                        θ                                            )                                                                                                          ⁢                                  ⁢                  (                                                    V                a                            =                                                                    V                    ′2                                    +                                                            (                                              2                        ⁢                        π                        ⁢                                                                                                  ⁢                                                  f                          s                                                ⁢                                                  L                          s                                                ⁢                        I                                            )                                        2                                                                        ,                          θ              =                              arcsin                ⁡                                  (                                      2                    ⁢                    π                    ⁢                                                                                  ⁢                                          f                      s                                        ⁢                                          L                      s                                        ⁢                                          I                      /                                              V                        a                                                                              )                                                              )                                    (        3        )            
When Ls=0, vin=V′ sin ωt is established, and the phase difference θ between vin and i (=I sin ωt) becomes zero, and the input power factor of the power receiving circuit 320 becomes 1. However, when Ls≠0, as illustrated in FIG. 33, there is a phase difference θ between vin and i, and it follows that the input power factor decreases.